The present invention broadly relates to pumps and, more particularly, to electromagnetic pumps for causing the movement of fluids that are electrically conductive.
It is frequently necessary or desirable to pump liquids that are either corrosive, should not be subjected to violent agitation, or tend to seep through small openings or cracks, or which, because of their chemical properties, should be kept completely enclosed and isolated from the atmosphere. This is particularly true in the case of pumps used for such liquid metals as sodium and sodium-potassium eutectic which are used as coolants in nuclear reactors.
In cases such as those above, mechanical pumps are generally unsatisfactory because of the requirements for moving blades or vanes and their associated bearings. These moving parts impose limitations on the types of materials which can be used, as well as the need for seals which ordinarily must not leak or permit the entrance of air. These considerations have led to the development of the so-called "electromagnetic" pump. This type of pump solves most of the problems associated with mechanical pumps when used to pump electrically conductive liquids such as mercury, sodium, potassium, or the like. However, such pumps have one serious drawback; namely, they are relatively inefficient. Indeed, efficiencies as low as 20% are not uncommon.
A typical example of a prior art conduction type of electromagnetic pump is found in U.S. Pat. No. 2,386,369. This patent describes a pump in which mercury is caused to flow along a channel by the reaction between an electric current passing through the mercury having a component perpendicular to the direction of flow of the mercury and a magnetic field having a component perpendicular both to the electric current and to the direction of flow. The pump duct is composed of dissimilar metals.
Another conduction type of electromagnetic pump is described in U.S. Pat. No. 2,686,474. This patent describes an electromagnetic pump for electrically conducting fluids such as liquid metals wherein the fluid is caused to flow along a duct in a gap in an iron circuit due to the interaction of mutually perpendicular components of flux or current in the field. This patent discusses improving the maximum pressure and efficiency of conduction-type pumps. The manner in which it is proposed such improvements be made is by looping the pump duct back through the air gap to reduce the distortion of the primary magnetic field due to the duct current.
Another linear conduction type of electromagnetic pump is described in U.S. Pat. No. 2,798,434. In accordance with the invention described therein, it is proposed that the distribution of the field flux in the pump throat may be made uniform and uniformly distributed by conducting the throat current across the top or bottom of the pump throat in a direction opposite the direction of the current through the fluid in the throat.
U.S. Pat. No. 3,263,283 relates to a continuous casting process and apparatus. The apparatus utilizes a multi-phase linear induction type of electromagnetic pump. This reference, however, does not suggest any means for improving the efficiency of such a pump.
U.S. Pat. No. 3,444,816 describes a conduction type of electromagnetic pump which is capable of pumping conductive liquid at a relatively high pressure and low flow rate. The pump described produces a magnetic field in a first direction across a gap filled with electrically conductive liquid. The pump also has electrodes which cause electric current to flow through the liquid in the gap at right angles to the direction of the magnetic field to cause pressure and flow of the liquid in a direction normal to both the magnetic and electric fields. Through the use of a narrow gap in the direction of the magnetic field, a high magnetic field strength is accomplished with magnets or magnetic coils of reasonable size. This produces a liquid space which is of small cross-sectional area in the direction perpendicular to current flow to produce a relatively high electrical resistance in the liquid such that the pump employs a relatively low electric current to produce a high fluid head.